The present invention relates to an improved, high energy storage cell.
Over the past several years, considerable effort has been expended to improve storage cells or batteries for use in numerous electronic devices. The energy content of each cell has been substantially increased so that the battery has a longer useful life and, in turn, needs to be replaced less frequently. Examples of the improved storage cells to which the present invention relates are shown in U.S. Pat. No. 3,985,573, issued Oct. 12, 1976, and U.S. Pat. No. 4,032,696, issued June 28, 1977, both of which are assigned to the assignee of the present application, and are incorporated herein by reference in their entirety. Both of these patents disclose bobbin-type liquid cathode cells using an alkali metal electrode, such as lithium, sodium or calcium with lithium being the preferred material. The storage cells also employ a powdered carbon electrode which may or may not be held together by a suitable binder. A nonaqueous cathode material such as thionyl chloride is used in the cell to facilitate the electrochemical reaction.
In the bobbin cells of the type described in each of the above patents, the metal electrode is consumed in the course of the electrochemical process. The cell is usually assembled with one of the electrodes contacting the inner wall of the container forming the outer shell of the battery and with a separator between this electrode and the other electrode. Lithium is used to form the anode of the cell and can be positioned as either the inner or outer electrode. As the electrochemical process takes place, the lithium electrode is consumed and the spacing between the electrodes will gradually increase, thereby increasing the internal cell resistance of the cell and, in turn, lowering the energy output of the cell. In order to compensate for this change in the physical dimensions of the cell in the course of the electrochemical process, the '573 patent employed a resilient, cylindrical cathode collector which could be compressed for insertion into the cell. The cathode collector would expand after insertion and continue to expand, maintaining pressure on the separator and the lithium electrode during the course of the electrochemical process. The '696 patent, on the other hand, placed the carbon electrode against the container wall lined with a separator. The lithium electrode was then added in segments to the center of the cell and was placed under spring pressure forcing the segmented lithium against the separator and carbon electrode during the course of the electrochemical process. Each of these cells were successful high energy cells.
Another patent of interest to the present invention is U.S. Pat. No. 3,796,606, issued Mar. 12, 1974, to G. Lehmann et al which is also incorporated herein by reference. In the bobbin cell disclosed in this patent, a first electrode material is placed against the inner wall of the container which forms one external terminal of the cell. A separator then lines the exposed surface of the first electrode. A sheet of lithium is then welded to the surface of a cylindrical spring. The composite spring/lithium metal is then compressed and inserted into the center of the cell. The spring is then released and allowed to expand, pressing the lithium electrode against the separator. The pressure would be maintained throughout the course of the electrochemical reaction as the lithium is depleted.
In each of the above cells, a means is provided for maintaining pressure on the electrodes during the course of the electrochemical reaction. Each of the cells, however, presented difficulties during the manufacturing process. In the '573 patent, the resilient carbon cathode collector had to be compressed in order to be inserted into the partially completed battery. In the '696 patent, the segmented lithium electrode reduced the lithium content of the battery and, in turn, the energy content and, also, presented difficulties in manufacturing because of having to handle the segmented electrode along with a spring. In the '606 patent, a cylindrical spring was used. However, it was difficult to contain the spring as a smooth cylinder was presented with no way to grip the edges in the course of the battery assembly process. For example, if the spring were grasped at the top to hold it in position, the bottom would have a tendency to spread open, inhibiting the entrance of the composite spring/lithium metal electrode into the battery. Even if an insertion tool, e.g., an insertion die, were used to assist in inserting the composite spring/lithium metal member, two problems would occur: (1) the lithium would tend to gall and to adhere to the tool, and (2) in order to provide adequate clearance during insertion for the tool between the cell separator and the composite spring/lithium metal member, the diameter of the composite member would have to be excessively reduced such that its ultimate spring recovery would be impeded.